1. Technical Field
The present invention relates to a ballpoint pen refill having an ink-accommodating tube containing an ink having a thixotropic property and a greaselike ink follower directly put in the ink-accommodating tube so as to be in contact with the rear end of the ink to prevent the reverse flow of the ink and capable of advancing together with the rear end of the ink as the ink is consumed.
2. Description of Related Art
A ballpoint pen refill has an ink-accommodating tube containing an ink having a thixotropic property and a greaselike ink follower directly put therein so as to be in contact with the rear end of the ink to prevent the reverse flow of the ink and capable of advancing together with the rear end of the ink as the ink is consumed.
The ink having a thixotropic property is consumed at a consumption rate higher than that at which the oil ink of the ballpoint pen is consumed. Generally, the ink-accommodating tube has a large diameter portion containing the ink and a small diameter portion holding a ballpoint pen tip which rotatably holds a ball. Some ink-accommodating tubes are of a two-section construction having a large diameter portion and a small diameter portion such as mentioned above, and other ink-accommodating tubes are of a three-section construction having a big diameter portion, a small diameter portion and a medium diameter portion connecting the large diameter portion and the small diameter portion.
When such a ballpoint pen refill is impacted, the ink-accommodating tube and the ink tend to slide relative to each other. Consequently, an impulsive force resulting from the weight of the ink acts on the ink follower if the ballpoint pen tip is directed upward or the same impulsive force acts on the ball if the ballpoint pen tip is directed downward.
When the impulsive force acts on the ink follower, the impulsive force can be absorbed by the viscosity of the ink follower and the physical performance of the ink-accommodating tube, such as the wettability of the inner surface of the ink-accommodating tube with the ink follower.
When the impulsive force acts on the ball, the impulsive force is borne only by a front end edge of the ballpoint pen tip formed by spinning or the like so as to hold the ball in the ballpoint pen tip. In a ballpoint pen tip having a small ball, the wall thickness of the front end edge of the ballpoint pen tip holding the small ball is small and an exposed portion of the ball projecting from the front end edge is small and, therefore, the edge of the front end edge is liable to come into contact with a paper sheet.
Consequently, the front end edge is worn and the ability of the front end edge to hold the ball lessens as the ballpoint pen is used and, eventually, the ball falls off the front end edge when an impulsive force acts on the ball. The applicant of the present patent application have previously proposed an improved ballpoint pen refill particularly for a retractable-type ballpoint pen which is carried around with its ballpoint pen tip directed downward, capable of eliminating the possibility of falling of the ball off the front end edge in Japanese Laid-Open Publication No.175078/1997. This previously proposed ballpoint pen refill has an ink-accommodating tube provided with a ballpoint pen tip in a front end portion thereof, and a partition wall disposed behind the rear end surface of the ballpoint pen tip and provided with an ink passage.
When fabricating a ballpoint pen refill including an ink-accommodating tube containing an ink having a thixotropic property and a greaselike ink follower, air is entrapped in the ink when filling the ink and the ink follower in the ink-accommodating tube. If air stays in the ballpoint pen tip or the like, the ink is unable to flow through an ink passage or the flow of the ink is obstructed, and the ink is unable to run properly. Therefore, air entrapped in the ballpoint pen refill must be discharged outside. In a stationary state, both the ink and the ink follower are highly viscous, air entrapped in the ballpoint pen refill is unable to flow and to escape naturally from the ballpoint pen refill even if the ballpoint pen refill is held with the ballpoint pen tip directed downward.
Therefore, the ballpoint pen refill is mounted on the rotor of a centrifuge with the ballpoint pen tip directed radially outward and the rotor of the centrifuge is rotated to force the ink toward the ballpoint pen tip by centrifugal force so that air entrapped in the ballpoint pen refill is discharged outside forcibly through the open rear end of the ink-accommodating tube.
In the ballpoint pen refill provided with the partition wall disposed behind the ballpoint pen tip, air staying in a front end portion of the ink-accommodating tube in front of the partition wall is stopped by the front end surface of the partition wall when the ballpoint pen refill is turned on the centrifuge and air stays in the front end portion of the ink-accommodating tube. It was found that the flow of air toward the open rear end of the ink-accommodating tube is obstructed. Air cannot be discharged outside through the open rear end of the ink-accommodating tube. Air blocks the ink passage formed in the partition wall or an ink passage formed in the ballpoint pen tip to cause the unsatisfactory flow of the ink.
The present invention, which has an ink-accommodating tube containing an ink having a thixotropic property and a greaselike ink follower capable of moving together with the ink as the ink is consumed and of preventing the reverse flow of the ink, has been made in view of the above-mentioned problems. It is an object of the present invention to provide a ballpoint pen refill which is formed in a structure that can prevent the action of an impulsive force on a ball resulting from the weight of the ink due to the movement of the ink and the ink-accommodating tube relative to each other and that can prevent air which is entrapped in the ink when filling the ink and the ink follower in the ink-accommodating tube from staying in the ink-accommodating tube during a deaeration process for removing air entrapped in the ink from the ink-accommodating tube.